1. Field of the Invention
The present invention relates to a light source used in a projector which projects an image on a screen. Further, the present invention relates to a projector using the projector light source, and in particular, to a liquid crystal projector using the a liquid crystal panel.
2. Description of the Related Art
Techniques for manufacturing a semiconductor device in which a semiconductor thin film is formed on a low cost glass substrate, for example a thin film transistor (TFT), have been developing rapidly. The reason is the fact that the demand for an active matrix type liquid crystal panel becomes high.
A thin film transistor (pixel TFT) is arranged in each of several hundred thousands to several millions of pixels arranged in a matrix state in an active matrix type liquid crystal panel (liquid crystal panel). Electric charges inputted to a pixel electrode on each pixel is controlled by the pixel TFTs.
Furthermore, projecting type display panels using the liquid crystal panel, namely liquid crystal projectors, are rapidly increasing their presence in the marketplace. Reasons which can be given for this include better color reproduction, smaller size, lighter weight, and lower power consumption with the liquid crystal projector compared to a projector using a CRT.
The liquid crystal projector performing color display projects images corresponding to red, green, and blue colors, respectively, on a screen, either at the same time or in order, and forms a color image by transmitting red, green, and blue colored light, contained in white light from a light source, through the liquid crystal panel either at the same time or in order.
A method of irradiating white light to pixels of the liquid crystal panel, of absorbing unnecessary colors from the colors red, green, and blue contained in the white light by color filters contained in the pixels, and of transmitting the desired color of light to the pixels can be given as a method of displaying a color image by the liquid crystal projector.
Further, a method of separating white light into three primary colors (red, green, and blue) and then transmitting each color of light through the pixels can also be given. A method of using two or three dichroic mirrors can be given as a method of separating white light from a light source into the three primary colors of light (red, green, and blue). As an example, a first dichroic mirror reflects only light in a red color (R) wavelength range, for example, from white light emitted from the light source, and transmits other colors of light. A second dichroic mirror reflects only light in a green color (R) wavelength range, for example, out of light transmitted through the first dichroic mirror, and transmits the other color of light. Only light in blue color wavelength range is transmitted through the first and the second dichroic mirrors. White color light irradiated from the light source can be separated into light of the three primary colors by using this type of structure. In addition, it is possible to separate white as color light from a light source into light of the three primary colors (red, green, blue) by using another known method.
High brightness and good color reproduction are required for an image displayed by the liquid crystal projector. The light source can be given as one of factors that determine the brightness of the liquid crystal projector image and its color reproduction.
Lamps such as a metal halide lamp, a xenon lamp, a halogen lamp, a low pressure mercury lamp, a high pressure mercury lamp, or a xenon flash tube are generally used for the light source of the liquid crystal projector.
The light emitted by each of the lamps has its own characteristic spectral distribution. The color of light emitted from a high pressure mercury lamp is a white color with a hint of yellowish green, and the brightness of the red color wavelength range is extremely low. If the light emitted from the high pressure mercury lamp is separated into the three primary colors (red, green, blue) of light, then the brightness of red color light will be considerably lower when compared to blue and green colored light.
Therefore, if the high pressure mercury lamp is used as is as the light source of the liquid crystal projector, in comparison with the desired color image, the image actually formed on the screen has a lower red color brightness relative to the brightnesses of blue and green colors.
When using the high color mercury lamp as the liquid crystal projector light source, a method of lowering the brightness of blue color and green color light contained in the white light from the high pressure mercury lamp to the same order as the brightness of the red color light using an optical system filter is conventionally performed. However, although the balance in brightness between the red, green, and blue colors of light becomes good, the overall brightness of the image displayed becomes low.
Further, in addition to the above method, a method of using light having a slightly shorter wavelength (orange color) than that of the color red as red colored light is conventionally performed in order to increase the brightness of the color red. In this case, however, even though the brightness becomes higher, the purity of the red color of the image displayed is low, and when a red color image is to be displayed, it gets displayed as orange in color and the reproduction deteriorates.
Not limited to the high pressure mercury lamp, the light emitted by other lamps such as the metal halide lamp, the xenon lamp, the halogen lamp, the low pressure mercury lamp, and the xenon flash tube which are generally used for the liquid crystal projector light source also possesses its own characteristic spectral distribution. Therefore, depending upon the light source, the image actually displayed on the screen has higher or lower brightness on any of the red, blue, or green colors compared to the desired image color. Further, in order to ensure balance in the brightnesses of red, blue, and green colors, the color purity of the light becomes low, so that the image color reproduction deteriorates, or the brightness of the entire image becomes lower.
Taking into account the above problems, an object of the present invention is to provide: a light source which can form an image having good balance in brightness between red, blue, and green colors, having high color purity of light, having high brightness overall, and displayed in well reproduced color on a screen; and a projector using the light source.
The present invention uses two or more lamps having differing light spectral distributions for a light source of a projector, in particular a liquid crystal projector. With the above structure, light with a wavelength range of low brightness emitted from one lamp is compensated by light emitted from the other lamp, and the light irradiated from the light source has good balance in brightness between red, blue, and green colors. The balance in brightness of red color, blue color, and green color light becomes good by the above structure, and it becomes possible to form an image having good color purity and high brightness overall on a screen.
For example, a lamp in which the red color brightness is lower than the brightnesses of blue and green colors, and a lamp in which the red color brightness is higher than that of blue and green colors are used as a single light source (light sources having the structure of the present invention are hereafter referred to as light source optical systems) in a liquid crystal projector. The red, blue, and green color brightness balance and the color reproduction, of an image displayed on a screen by the liquid crystal projector is improved, and the overall brightness of the image can be increased by the above structure.
The structure of the present invention is shown below.
According to the present invention, there is provided a light source optical system comprising a first lamp which emits a first light, a second lamp which emits a second light, and a condensing optical system which synthesizes the first light and the second light and forms irradiation light, characterized in that
the first light and the second light have mutually differing spectral distributions.
According to the present invention, there is provided a light source optical system comprising a first lamp which emits a first light, a second lamp which emits a second light, a first lamp condensing system, a second lamp condensing system, and a condensing optical system, characterized in that:
the first light and the second light have mutually differing spectral distributions; and
the first light and the second light, after being adjusted so as to have a uniform illumination distribution on an irradiation surface by the first lamp condensing system and the second lamp condensing system, respectively, are synthesized by the condensing optical system so as to become irradiation light.
According to the present invention, there is provided a light source optical system comprising a first lamp which emits a first light, a second lamp which emits a second light, and a condensing optical system, characterized in that:
the first light and the second light have mutually differing spectral distributions;
light having a specific wavelength range is separated from the first light by a means of light separation;
the brightness of the light having the specific wavelength range is adjusted by an optical system filter; and
the brightness-adjusted light having the specific wavelength range and the second light are synthesized by the condensing optical system so as to become irradiation light.
According to the present invention, there is provided a light source optical system comprising a first lamp which emits a first light, a second lamp which emits a second light, a first lamp condensing system, a second lamp condensing system, and a condensing optical system, characterized in that:
the first light and the second light have mutually differing spectral distributions;
light having a specific wavelength range is separated from the first light by a means of light separation;
the brightness of the light having the specific wavelength range is adjusted by an optical system filter; and
the brightness-adjusted light having the specific wavelength range and the second light, after being adjusted so as to have a uniform illumination distribution on an irradiation surface by the first lamp condensing system and the second lamp condensing system, respectively, are synthesized by the condensing optical system so as to become irradiation light.
The means of light separation may be a dichroic mirror.
The means of light separation may be a color filter.
The first lamp and the second lamp may be each one lamp selected from the group consisting of a halogen lamp and a high pressure mercury lamp.
According to the present invention, there is provided a three panels type liquid crystal projector having the above light source optical system.
According to the present invention, there is provided a single panel type liquid crystal projector having the above light source optical system.
According to the present invention, there is provided an overhead projector (OHP) having the above light source optical system.